You can not remove any phpbb for forumotion links in the footer or your forum will be in violation and be shut down.

Now you can pay to have them removed, so just because you may see a forumotion forum with it gone dose not mean they did not pay to have them removed.

However, if you feel someone is removing the footer and in violation then you can always report the forum to forumotion litigation's, then if they are indeed in violations for removing the footer then litigation's either warn them and tell them not to do it again, or most likely just shut the forum down.